Non-mechanical printer or copier means comprising an exposure means arranged in the development region

ABSTRACT

An exposure means is provided between a development region and a carrier stripping drum that removes carrier particles, being provided inside the developer station of a non-mechanical fast data printer means. The exposure means illuminates and thereby discharges the highly charged and non-toner-covered regions of the surface of a charge image carrier. The adhesion of negative carrier particles of the developer mix to the non-exposed regions of the surface of the charge image carrier is thus reduced, so that they can be easily stripped from the surface of the charge image carrier by the following carrier stripping drum.

BACKGROUND OF THE INVENTION

The invention is directed to a non-mechanical printer or copier meanshaving a developing region for developing a charge region generated on acharge image carrier with the assistance of an exposure means using adeveloper mix of toner particles and carrier particles.

In copier equipment technology and in non-mechanical fast data printersthat operate based on the principle of electrophotography, charge imagesare generated on a charge image carrier, for example on aphotoconductive drum, and are subsequently inked with a colored powder,toner in a developer station. The toner images are subsequentlytransferred onto normal paper given employment of a photoconductive drumand are fixed there.

As a rule, a two-component developer is employed for developing, thisbeing composed of ferromagnetic carrier particles and of colored tonerparticles. The developer mix, for example, is conducted past the chargeimage on the charge image carrier with a magnetic brush arrangement, thetoner particles adhering to the charge image as a result ofelectrostatic forces. The magnetic brush arrangement is thereby composedof a rotatable hollow cylinder in whose interior a plurality of rows ofstationary permanent magnets are arranged.

A plurality of magnetic brush arrangements can be provided in onedeveloper station. For example, one magnetic brush arrangement can servethe purpose of transporting the developer mix past the charge imagecarrier. This magnetic brush arrangement shall be referred to below as adeveloper drum. A further magnetic brush arrangement can be employed inorder to transport the developer mix out of the inside of the developerstation to the developer drum. Such a magnetic brush arrangement or anyother arrangement that effects such a transport of developer mix isthereby referred to below as a transport drum.

Adjoining the development region, it is also standard to remove thecarrier particles of the developer mix sporadically adhering to thecharge image carrier from the charge image carrier with the assistanceof a carrier stripper roller likewise fashioned as magnetic brush drumand to return these carrier particles to the developer mix.

Developer stations wherein developer mix for inking the charge images onthe charge image carrier with the assistance of the magnetic brushprinciple are employed are disclosed by German Patent 31 19 010 andcorresponding U.S. Pat. No. 4,461,238.

As already set forth, a significant problem in non-mechanical printer orcopier devices operating according to the principle ofelectrophotography is achieving the complete removal of the carrierparticles from the inked charge image following the development region.In standard non-mechanical printer or copier devices that work accordingto the reversal development method and wherein the regions of the chargeimage carrier discharged via a character generator are inked, there isthe risk that the carrier particles will agglomerate to those regionsthat are still charged and that are not to be inked. The completeremoval of these carrier particles with the assistance of a carrierstripper drum is difficult.

When these carrier particles are not completely removed or,respectively, when these carrier particles are entrained by thephotoconductive layer of the photoconductive drum up to the actualtransfer station, then the transfer event is deteriorated. Inparticular, this leads to light spots and other disturbances in theprinted format.

GB-A- 15 24 543 and corresponding U.S. Pat. No. 3,920,329; discloses anelectrophotographic copier means that comprises an isorunningdevelopment station. The development station is followed by a carrierstripper drum that serves the purpose of removing excess developer mixfrom the charge image carrier. A corona discharge station is arrangedbetween the carrier stripper drum and the development station. Coronadischarge stations, however, have the disadvantage that they act both onthe inked regions as well as on the non-inked regions of the chargeimage.

In order to facilitate the transfer of the toner particles onto therecording medium, U.S. Pat. No. 3,424,615 and DE-A- 34 01 992 disclosethat an illumination means in the form of carrier lamps be arranged inmoving direction of the photoconductor preceding the actual transferstation.

SUMMARY OF THE INVENTION

It is an object of the invention to fashion a non-mechanical printer orcopier means of the species initially cited such that a high printingquality is possible given high process speed and use of a developer mixhaving a long useful life.

In a non-mechanical printer device of the species initially cited, thisobject is achieved in that an illumination means for a charge imagecarrier is arranged between a development region and means for removingthe carrier particles in the development station itself, saidillumination means discharging by illumination the highly charged andnon-tonered regions of the charge image carrier.

The illumination means generates a largely uniform charge image on thecharge image carrier preceding the transfer station in the printer thatfollows the actual carrier stripper means for the carrier particles andfollows the carrier stripping means. This "image'wise" discharge thusnot only facilitates the removal of the carrier particles from thephotoconductive drum by reducing the electrostatic forces of adhesionbut it also promotes the transfer printing of the toner image onto thepaper web in the transfer station.

In order to guarantee the same penetration depth of the light into thesurface of the charge image carrier as the light that is controlled incharacter-dependent fashion that generates the charge image,approximately the same spectral distribution as for the light of thecharacter generator is recommended for the light of the exposure means.

When, for example, a light-emitting diode comb is employed as acharacter generator, then a similarly structured illumination means isalso recommended for the exposure means.

The illumination also makes it possible to prevent memory effects on thecharge image carrier that disturb the printed format due to chargeimages that are not completely quenched.

In an advantageous embodiment of the illumination means, the lightsource is surrounded by a light-transmissive, motor-driven protectivedrum, whereby this protective drum can be composed of a plexiglass tube.The illumination means comprising its protective tube is therebyarranged inside the developer station, namely in the proximity of thelast developer drum in the transport direction of the charge imagecarrier, whereby it is continuously cleaned of adhering mix particlesvia this developer drum during operation.

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows an embodiment of the invention and this shall be setforth in greater detail below by way of example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic sectional view of a developer station in anon-mechanical fast-printer means comprising the illumination means ofthe invention. A photoconductive drum 10 is arranged as a charge imagecarrier in a printer means not shown in greater detail that operatesaccording to the electrophotographic principle. A charge image isapplied to this photoconductive drum 10 in a known fashion via anexposure means that is controlled in character-dependent fashioned andthis charge image is then inked with the assistance of the illustrateddeveloper station. The inking thereby ensues according to the reversaldevelopment principle wherein the regions discharged by the exposure areinked with the assistance of a developer mix 11 containing tonerparticles and carrier particles. After traversing the developer station,the charge images composed of colored toner particles are transferredonto paper in the standard way.

The developer station is essentially composed of a supply chamber 12 towhich developer mix 11 is supplied via a filling aperture 13 comprisinga drum of expanded material arranged therein as a metering means. Anelectromotively driven conveyor drum in the form of a paddle wheel drum14 that comprises spoke-like paddles 15 for conveying the developer mix11 is situated at the floor of the supply chamber 12. The supply chamber12 is closed off from the photoconductive drum 10 by four developerdrums 16, 17, 18 and 19. These developer drums arranged along thecircumference of the photoconductive drum are situated at the tightspacing of about 1 through 2.5 mm from the surface of thephotoconductive drum 10 and operate according to the magnetic brushprinciple. They are essentially composed of hollow cylinders 20 whichare constantly driven via electromotive means and are of, for examplealuminum having a knurled surface and having magnet arrangements 21arranged therein. The hollow cylinders 20 are thereby charged with abias voltage that exhibits approximately the size of 20 through 50% ofthe charge potential at the photoconductive drum 10. Given employment ofa selenium photoconductive drum 10 having a charge potential of 400through 1000 volts, the bias voltage has the size of 100 through 500volts.

Depending upon the moving direction of their hollow cylinders, thedeveloper drums 16, 17 and 18 are fashioned as what are referred to asisorunning developer drums. In the isorunning developer drums, themoving direction of their hollow cylinders 20 corresponds to the movingdirection of the surface of the photoconductive drum 10 in the region ofa developing gap 22 formed by the hollow cylinder 20 and the surface ofthe photoconductive drum 10. The last developer drum 19 is fashioned asa counterrunning developer drum wherein the hollow cylinder 20 moves ina direction opposite that of the photoconductive drum 10 in thedevelopment gap 22.

The transport of the developer mix 11 thereby ensues according to thearrows shown in FIG. 1 the figure such that the developer mix 11 isoffered to the first isorunning developer drum 16 from the mix sumpfloor of the supply chamber 12 via the paddle wheel drum 14. A meteringdoctor 23 thereby defines the height of the carpet of developer mix onthe first isorunning drum 16 and, thus, on the following isorunningdrums 17 and 18 as well. Since the developer mix has developed thecharge image contained on the photoconductive surface three times withconsiderably higher speed than the photoconductive surface (about 1.5times the process speed), namely with the assistance of the isorunningdeveloper drums 16, 17 and 18, the developer mix transfers from thethird isorunning drum 18 onto the under side of the significantlyslower, fourth counterrunning developer drum 19 that is driven in theopposite direction. A major part of the developer mix 11 is stripped offthe fourth developer drum 19 by a further metering doctor 24 and theremaining developer mix is transported to the surface of thephotoconductive drum 10 to develop the charge image a final time incounterrun. The spacings of the developer rollers advantageously lieunder 2.5 mm, whereby the developing gap 22 has a width of 1 through 2.5mm. The developer mix 11 must be conveyed through this development gap22 with optimally high density. The density of the developer mix 11 mustthereby be selected such that, first, the latent charge image iswell-inked and, second, such that the surface of the charge imagecarrier is not damaged as a result of excessively great squeezing.

In order, first, to be able to transport the developer mix 11 with theassistance of the developer drums but, on the other hand, in order to beable to enable an agglomeration of the toner particles on the chargeimage, the surface of the developer drums, as already set forth, ischarged with a bias voltage of about 20 through 50% of the chargepotential.

An illumination means in the form of a light-emitting diode strip orlight-emitting foil 25 that is accomodated in a protective drum 26composed of a transparent, rotating plexiglass tube is situated abovethe last developer drum fashioned as a counterrunning developer drum 19.Rotation and spacing from the counterrunning developer drum 19 areadapted such that the surface of the plexiglass tube 26 is continuouslycleaned of the developer mix 11 and a light exit region 27 of thelight-emitting diode strip 25 is only slightly attenuated by adheringtoner dust. The light-emitting diode strip 25 thereby generates aspectral light that approximately corresponds to the light of thecharacter generator and is, for example, a LED comb.

Further, a carrier stripper drum 28 operating according to the magneticbrush principle in accord with the developer drums is situated above theillumination means 25. This carrier stripping drum 28 lifts the carrierparticles of the developer mix 11 from the surface of thephotoconductive drum 10 in collaboration with the illumination means andreturns them to the developer mix 11 via a correspondingly fashionedguide channel.

Via the light-emitting diode strip 25, the illumination means levels thecharge image in that it illuminates the highly charged (about 400through 1000 volts) and non-toner-covered regions of the surface of thephotoconductive drum 10 and thereby discharges them down to a residualvoltage of less than 50 volts that thus corresponds to the dischargevoltage of the character generator. The adhesion of negative carrierparticles of the developer mix to the non-exposed regions of the surfaceof the photoconductive drum 10 is thus reduced, so that they can bestripped from the surface of the photoconductive drum 10 by thefollowing carrier stripper drum 28 and can be returned into thedeveloper station. Simultaneously memory effects due to charge images onthe surface of the photoconductive drum that were not completelyquenched can be prevented by the illumination means.

The illumination means generates a largely uniform charge image on thecharge image carrier preceding the carrier stripper means and thefollowing transfer station in the printer. The charge image carriertherewith is at a uniform residual charge voltage of about 50 volts.This "image-wise" discharging thus facilitates not only the removal ofthe carrier particles from the photoconductive drum but it also promotesthe transfer of the toner image onto the paper web in the transferstation. In order to guarantee the same penetration depth of the lightinto the surface of the charge image carrier as the light that iscontrolled in character dependent fashion that generates the chargeimage, the light of the exposure means has approximately the samespectral structure as the light of the character generator. When, forexample, a light-emitting diode comb is employed as the charactergenerator, then a similarly structured illumination means isrecommendable. Instead of a LED line, a light-emitting foil can also beemployed.

The illumination means is surrounded by a suction means that acts on theregion between the carrier stripper drum 28 and the protective drum 26via a suction channel 29 extending along the illumination means. Thissuction channel 29 is in communication with a suction blower (notillustrated here) via a suction collecting channel 30. This airextraction between the plexiglass tube (protective drum) 26 comprisingthe illumination means and the carrier stripping drum 28 generates alocal under-pressure and, thus, free toner dust that is not bonded bythe charge image is collected in a container. The free toner dust canthus not be entrained upward out of the developer station by thephotoconductive drum 10. Carrier particles stripped by the carrierstripping drum 28 and developer mix stripped by the metering doctor 24of the counterrunning developer drum are returned into the supplychamber 12 via baffle plates 31.

An emptying aperture 32 via which used developer mix is suctioned offafter a defined operating time is situated at the floor of the supplychamber 12.

We claim:
 1. A non-mechanical printer or copier device, comprising:acharge image carrier in the printer or copier device; an exposure meansin the printer or copier device for exposing said charge image carrierwith a character image to produce a charge image on said charge imagecarrier; a development region in the printer or copier device fordeveloping by reversal development the charge image generated on saidcharge image carrier to thereby form charged and discharged regions onsaid charge image carrier, said development region utilizing a developermix composed of toner particles and of carrier particles, saiddevelopment region includingdevelopment rollers positioned relative tosaid charge image carrier to apply the developer mix to regions of thecharge image that are discharged by the character image exposure, and ameans for removing carrier particles from the charge image carrier, saidmeans following the development rollers in a moving direction of thecharge image carrier; an illumination means following said developmentregion for illuminating the charge image carrier, said illuminationmeans discharging by exposure highly charged and non-tonered regions ofthe charge image carrier, light generated in the illumination meansroughly corresponding in terms of its spectral composition to light ofthe exposure means; and the illumination means being arranged inside thedevelopment region between the means for removing the carrier particlesof the developer mix and the development region so that the carrierparticle are removable by said means for removing while leaving thetoner particles adhered to the charge image carrier for image transfer.2. A non-mechanical printer or copier device according to claim 1,wherein aid exposure means comprises a light source surrounded by alight-transmissive, motor-driven protective drum; and furthercomprising: cleaning means for cleaning the protective drum of mixparticles adhering thereto during operation.
 3. A non-mechanical printeror copier device according to claim 2, wherein said protective drum is aplexiglass tube.
 4. A non-mechanical printer or copier device accordingto claim 2, wherein said development region includes a developer drumarranged relative to said protective drum such that a surface of theprotective drum is continuously cleaned of developer mix.
 5. Anon-mechanical printer or copier device, comprising:a charge imagecarrier in the printer or copier device; an exposure means in theprinter or copier device for exposing said charge image carrier with acharacter image to produce a charge image on said charge image carrier;a development region in the printer or copier device for developing byreversal development the charge image generated on said charge imagecarrier to thereby form charged and uncharged regions on said chargeimage carrier, said development utilizing a developer mix composed oftoner particles and of carrier particles, said development regionincludingdevelopment rollers positioned relative to said charge imagecarrier to apply the developer mix to regions of the charge image thatare discharged by the character image exposure, and a means for removingcarrier particles from the charge image carrier, said means followingthe development rollers in a moving direction of the charge imagecarrier; an illumination means following said development region forilluminating the charge image carrier, said illumination meansdischarging by exposure highly charged and non-tonered regions of thecharge image carrier, light generated in the illumination means roughlycorresponding in terms of its spectral composition to light of theexposure means, the illumination means being arranged inside thedevelopment region between the means for removing and the developmentregion; and a suction means for suctioning off developer mix parts thatare not bonded to the charge image carrier, said suction means beingbetween the illumination means and the means for removing the carrierparticles.